With new applications in these fields, the bandwidth requirements are increasing regularly while being accompanied by a demand to reduce costs, and therefore to simplify the RF signal reception chain.
A plurality of combined effects are accentuating the need for sampling and conversion systems for analog and digital signals.
In order to digitally process the received signals, the reception chains of these receivers need to have analog/digital conversion functions.
Thus, telecommunications require larger and larger bandwidths in order to allow the transmission of dense data streams, notably in wireless local area networks (WLAN). There may be considered to be a law for data transmission equivalent to Moore's Law, namely that the bit rate of wireless communications doubles every 18 months, rapidly exceeding a rate of 1 Gbps.
Because of the intrinsic limitations of the bandwidth available to analog/digital converters being developed, without other alternative technologies having yet been suggested, microwave reception chains require complex and expensive transposition functions.
In particular, current semiconductor-based technologies do not make it possible to provide analog/digital encoders operating above 2 to 3 GHz with a large dynamic range, often lying beyond a signal-to-noise ratio of 50 dB. It is conventional to introduce microwave mixing functions into the reception chain in order to transpose the received signals into the frequency band compatible with the input of an encoder.
When the input frequencies are very high, it is necessary to resort to a plurality of mixing stages, which significantly increases the complexity of microwave reception chains.
Optically controlled electronic devices can be used to carry out the switching or sampling functions required in order to produce, notably, converters.
In the scope of use in an analog reception system, a user generally seeks a device whose performances in terms of dynamic range, insertion losses and noise are optimized, and the optical control power of which is therefore as low as possible. In the case of a photoswitch, in particular, this leads to a device whose two optically controlled states, the on state and the off state, are very different in terms of transmission, this difference being several tens of decibels (dB). Such a switch may be defined as a device having two electrodes representing an input port and an output port, which are deposited on a photoconductive substrate, as well as an interaction region consisting of the region of the substrate which separates the two ports and which, under the effect of a light wave, ensures electrical continuity between the two ports. The control light wave is generally conveyed by means of an optical fiber to the region of the component on which it interacts (interaction region) in order to control the operation of the component. Optimization of the optical control power is obtained by using systems making it possible to focus all of the light into the interaction region, with limitations which are of the order of 10 μm for a single-mode fiber and 50 μm for a multimode fiber. The literature reports a variety of research into the production of photoswitches with illumination using a high optical power, having an ultrafast operating mode, the time involved being of the order of one picosecond.
However, devices produced to date have characteristics and performances which limit the working frequency to frequencies compatible with the best contrast between the on state and the off state, denoted by ON/OFF. Thus, current devices are limited to frequencies of the order of 1 to 2 GHz, their characteristics and performances being as follows:                low ON/OFF contrast of the order of from 3 dB to 10 dB at a frequency of 20 GHz;        insertion losses of the order of 30 dB;        high optical control power, of the order of 100 mW on average.For a given semiconductor, reduction of the optical control power requires far smaller dimensions in the illuminated region, these dimensions being for example of the order of nanometers.        